Method of copper-plating metal surfaces



United States Patent 56 METHOD OF COPPER-PLATING METAL SURFACES WennemarStrauss, Dusseldorf Benrath, Germany, as-

signor to Dehydag, Deutsche Hydrierwerlie G.m.b.l-I., Dusseldorf,Germany, a corporation of Germany No Drawing. Application September 28,1954 Serial No. 458,983

Claims priority, application- Germany February 20, 1954 9 Claims. (Cl;204-32) This invention. relates to a method of copper-plating metalsurfaces, and more particularly to a: method of copper-plating thesurfaces of objects made of nonprecious metals.

The prior art discloses a great number of processes for depositingcopper plates uponthe surfaces of metal objects. In general, theseprocesses comprise first depositing a thin base coating of copper on themetal surface by immersing the object in a solution of a suitable coppersalt containing a cyanide compound and finally depositing the desiredultimate copper plate upon the pre-treated surface either by thewell-known dipping process or by electrolysis. The preliminary step ofproviding the metal surface with a base coating of copper priortoapplying the final copper plate is considered by the art to beindispensable to the production of good copper plates by electrolytic aswell as other means. It is obvious, however, that this preliminarytreatment renders the production of copper plated articles costly andthat a method which will produce a high grade copper plate without suchpro-treatment will make copper plated articles of all typesreadilyavailable to industry and the general public at a reduced costand in quantities greater than heretofore.

It is therefore an object of the present invention to provide a methodfor copper-plating metal objects which does not require the depositionof a'thin base coating of copper prior to the deposition of the finalcopper plate on the surface of such objects.

Another object of this invention is to provide a method of depositing acopper plate upon the surface of objects made of non-precious metalswhereby the final copper deposit can be applied directly to the cleanmetal surface of such objects.

Other objects and advantages will become apparent as the description ofmy invention proceeds.

I have found that objects made of non-precious metals such as iron,electrochemicallyactive steel, zinc, alumi num, and the like, can becopper-plated in an acid plating bath directly and without providingthem with a preliminary'thin copper deposit by contacting such objectsprior to the plating step, preferably immediately prior thereto, with anacid pickling bath which contains an inhibitor having a stronginhibiting effect.

The inhibiting effect of a compound suitable for use as an inhibitor inconjunction with the surface treatment of metal objects in acid picklingor plating baths can be defined as its capability of reducing the amountof hydrogen liberated by the attack of the acid bath upon the metalsurface. Thus, the inhibiting elfect of an inhibitor for pickling andelectroplating baths is to a certain degree equivalent to itscorrosion-preventing effect and can be expressed in terms of thefractional amount of the maximum amount of hydrogen liberated by an acidbath which does not contain a corrosion-preventing additive. The largestamount of hydrogen liberated by the attack of an acid pickling orplating bath-when no inhibitor is added corresponds to acorrosion-preventing effect of By adding inhibitors to such baths theamount of hydrogen ice . 2* liberated due to the attack of the acid bathon the metal can be reduced to practically zero, which'corresponds'to aninhibiting or corrosion-preventing effect of Compounds used asinhibitors within the scope of my invention have an inhibiting effectofat least 50%, which is termed a strong inhibiting effect.

While the theory of the action of inhibitors in acid pickling andplating baths is still unsettled, it is believed that inhibitingcompounds are characterized in that they retard the electrochemicalexchange on the metal surface and prevent the combination of the metalwith oxygen, both by adsorption.

In the pickling bath the adsorptive action of inhibiting compounds addedto the acid pickling bath results in minimizing the attack of thepickling solution on the virgin metal surface without appreciablyretarding the rate of dissolution ofsurface scale, rust or dirt on themetal surface.

In the plating" bath the ads'or-ptive action of inhibitors and theretardation caused thereby result in a homogeni- Zation of the metaldeposit which, in turn, produces metal deposits which are bright, adherewell to the metal surface, and are highly ductile.

In addition, it was found that suchinhibitors have a definiteoxidation-retarding effect in the pickling bath.

Compounds which are suitable for use as inhibitors in the acid picklingbath and obviate the deposition of thin base coatings of copper on themetal objects prior to the application of the final copper plate thereoninclude organic acyclic or cyclic oxygen-, sulfuror nitrogen-containingcompounds such as, for example, phenols, alcohols, aldehydes, ketones,sulfonic acids, sulfides, disulfides, sulfoxides or sulfones, aliphatic,cycloaliphatic, aromatic or heterocyclic bases, as Well as quaternaryammonium salts and other onium compounds, alkanolamines, especiallytriethanolamine andits salts, thiourea and its derivatives, andderivatives of guanidine and the like.

The adhering qualities of copper deposits applied to metal surfacestreated in pickling baths containing the above inhibitors can be furtherimproved by adding to the pickling bath inorganic or organic reducingagents suchas, for example, bivalent tin chloride, sodium sulfite,sodium bisulfate, hydrazine sulfate and the like.

I have further found that the quality of final copper deposits applieddirectly to metal surfaces of objects made of non-precious metals,pre-treated in the above manner,

can be improved by adding to the plating bath certain brightening agentswhich not only enhance the brightness of the copper deposit, but alsoact as inhibitors by retarding the electrochemical exchange on the metalsurface by adsorption. Examples. of brightening agents which have suchdual characteristics are organic sulfonic acidsor their salts having thegeneral structural formula aniline, lactic acid, as well as molasses,syrup, starch,

gelatine, glue and many others.

Finally, I have found that objects made of non preciousmetals can becopper-plated immediately, after pre-treat;

ment with a pickling bath and'without depositing a thin,

pre-coating of copper in a cyanide bath by using one and the sameadditive for the pickling bath and in the plating bath. Theprerequisite, however, is that such an additive must act as an inhibitorwith a strong inhibiting efiectin thepicklingbath and as a brighteningagent and as an inhibitor with a strong inhibiting efiect in the platebath. Examples of compounds which meet this requirement are thefollowing sulf-onic acids, which contain a carbon atom bondedexclusively to a groupof hetero atoms:

Betaine salts of isothiourea-S-butane-w-sulfonic acid Betaine salts ofN-phenyl-isothiourea-S-butane-w-sulfonic acid2-mercaptobenzothiazole-S-propane-w-potassium sulfonate Thiocyanicacid-S-n-propylester-w-sodium sulfonate2-thiobenzooxazole-Spropane-w-sodium sulfonate2-thiometoxazine-s-butane-w-potassium sulfonateN,N-dimethyl-dithiocarbamic acid-n-propylester-w-sodium sulfonateN,N-pentamethylene-dithiocarbamic acid-n-propylester-wsodium sulfonateN-butyl-dithiocarbamic acid-n-butylester-w-sodium fonateN-p-tolyl-dithiocarbamic sulfonate Dithiocarbamicacid-n-propylene-w-potassium sulfonate S-phenyl-trithiocarbonicacid-n-propylester-w-sodium sulfonate Trithiocarbonicacid-bis-propylester-w-sodium sulfonate Isopropyl-xanthogenicacid-n-butylester-w-sodium sulfonate n-Butyl-xanthogcnicacid-n-propylester-w-sodium sulfonate Carbaminothiolacid-n-propylester-potassium sulfonate and the like.

In place of the sodium or potassium salts of the above compounds, thecorresponding salts of other inorganic or organic basic elements orcompounds can be used equally as effectively.

Within the scope of my invention, the final copper deposit may beapplied directly to the pickled metal surface with the aid of thewell-known dipping process or also by the usual electroplating processemploying an electric current.

Aside from the addition of the above-described additives to the picklingbath and/or the plating bath in accordance with my invention, themethods usually ernployed in copper-plating metal objects need not bechanged. For example, the basic pickling bath consists of the usualinorganic or organic acids or acid salts, particularly sulfuric acid,and the pickling and plating baths may also contain the usual wettingagents. The plating bath may also contain any of the well-known agentswhich promote the formation of smooth copper plates as well as otherbrightening agents and porosity reducing agents. The basic plating bathsmay consist of any of the well-known and usually employed copper saltsolutions.

The method in accordance with my invention may be employed incopper-plating any non-precious metal such as iron, electrochemicallyactive steel, zinc, aluminum, magnesium, and alloys thereof.

The following examples will enable persons skilled in the art tounderstand my invention more completely. However, it is understood thatmy invention is not limited to the particular examples cited below.

sul-

acid-n-propylester-w-potassium Example I Sheet iron was first pickled ina pickling bath consisting of a 2 N-sulfuric acid solution andcontaining 0.1% to 0.5% dibenzylsulfide as an inhibitor. Thereafter thepickled sheet iron was electroplated in a copper sulfate solutioncontaining 0.5 -gm./liter dibenzylsulfoxide and 0.1 gm./liter thiourea,at room temperature and with a current density of 3 amps./dm. The copperdeposit 4 produced thereby adhered well to the surface of the sheet11011.

Example II Objects made of iron were pickled in a pickling bath of 2n-sulfuric acid containing 0.1% to 0.5% dibenzylsulfoxide as aninhibitor. Subsequently the pickled metal objects were electroplated ina copper sulfate bath which contained 0.5 gm./literN,N-dimethyl-dithiocarbamic acid-n-butylester-w-sodium sulfonate, atroom temperature and with a current density of 4 amp./dm. The copperdeposits produced thereby had excellent adhering properties.

Example Ill Objects made of sheet iron were pickled for 1 to 10 minutesin a pickling bath containing 1 gm./liter N,N- diethyl-dithiocarbamicacid-n-propylester-w-sodium sulfonate as an inhibitor. The pickled sheetiron objects were then copper plated at room temperature and with acurrent density of 5 amp./dm. in a copper sulfate solution whichcontained 1 gm./liter of N,N-diethyl-dithiocarbamicacid-n-propylester-w-sodium sulfonate as a brightening agent andinhibitor. The copper deposits produced thereby adhered very well to themetal surface and were bright and lustrous.

Example IV Sheet iron was pickled in a 2 N-sulfuric acid solution whichalso contained 1 gm./liter of the betaine salt ofisothiourea-S-propane-w-sulfonic acid as an inhibitor. Subsequently thepickled sheet iron was immersed for 2 minutes in a copper sulfatesolution which also contained 1 gm./liter of the above betaine salt as abrightening agent and inhibitor. A bright and well-adhering copperdeposit was produced thereby on the surface of the sheet iron, which wassufiicient for a variety of uses and further treatment.

A few of these dip-plated sheets were then further copper-plated byelectrolysis in a copper sulfate bath containing 1 gm./liter of thebetaine salt of isothiourea-S- propane-w-sulfonic acid. The copperdeposits obtained Objects made of sheet iron were pickled in a 2N-sulfuric acid solution containing 5 gm./liter bivalent tin chlorideand 1 gm./liter N,N-pentamethylene-dithiocarbamicacid-n-propylester-w-sodium sulfonate as an inhibitor. The pickled sheetiron objects were then dipped in a copper sulfate bath containing 1gm./liter of N,N- pentamethylene dithiocarbamicacid-n-propylester-w-sodium sulfonate as a brightening agent andinhibitor. As in Example IV, the copper deposits produced thereby hadexcellent brightness properties and adhered to the metal surfaces evenmore completely than those obtained in Example IV. A few of thesedip-plated objects were then electroplated in a copper sulfate bath asin Example IV. The copper deposits obtained were bright and lustrous andadhered very well to the surface of the objects.

While I have illustrated certain specific embodiments of my invention, Iwish it to be understood that certain changes and variations may be madewithout departing from the spirit of my invention and the scope of thefollowing claims.

I claim:

1. The method of producing copper deposits on surfaces of metal objects,said metal being selected from the group consisting of iron, zinc,aluminum and electrochemically active steels, which comprises picklingsaid objects in an acid pickling bath containing dibenzylsulfide as aninhibitor, and thereafter applying the final copper plate directly tothe pickled objects on which a layer of inhibitor from said picklingbath solution remains adherent by electroplating said objects in an acidsolution of copper sulfate, said solution containing small amounts ofdibenzylsulfoxide and thiourea.

2. The method of producing copper deposits on surfaces of metal objects,said metal being selected from the group consisting of iron, zinc,aluminum and electrochemically active steels, which comprises picklingsaid objects in an acid pickling bath containing dibenzylsulfoxide as aninhibitor, and thereafter applying the final copper plate directly tothe pickled objects on which a layer of inhibitor from said picklingbath solution remains adherent by electroplating said objects in an acidsolution of copper sulfate, said solution containing small amounts ofN,N-dimethyl-dithiocarbamic acid n-butylester-w-sodium sulfonate.

3. The method of producing copper deposits on surfaces of metal objects,said metal being selected from the group consisting of iron, zinc,aluminum and electrochemically active steels, which comprises picklingsaid objects in an acid pickling bath containing an inhibitor compoundhaving an inhibiting effect of at least 50% and thereafter applying thefinal copper plate directly to the pickled surface of said objects towhich a quantity of pickling bath solution remains adherent by electroplating said objects in an acid solution of a copper salt.

4. The method of producing copper deposits on surfaces of metal objectssaid metal being selected from the group consisting or iron, zinc,aluminum and electrochemically active steels, which comprises picklingsaid objects in an acid pickling bath containing an inhibitor having aninhibiting effect of at least 50% and thereafter applying the finalcopper plate directly to the pickled surface of said objects to which aquantity of pickling bath solution remains adherent by electroplatingsaid objects in an acid solution of a copper salt, said solutioncontaining a brightening agent.

5. The method of producing copper deposits on surfaces of metal objects,said metal being selected from the group consisting or iron, zinc,aluminum and electrochemically active steels, which comprises picklingsaid objects in an acid pickling bath containing an inhibitor having aninhibiting effect of at least 50% and thereafter applying the finalcopper plate directly to the pickled surface of said objects to which aquantity of pickling bath solution remains adherent, by electroplatingsaid objects in an acid solution of a copper salt, said solutioncontaining an inhibitor.

6. The method of producing copper deposits on surfaces of metal objects,said metal being selected from the group consisting or iron, zinc,aluminum and electrochemically active steels, which comprises picklingsaid objects in an acid pickling bath containing an inhibitor having aninhibiting effect of at least 50%, and thereafter applying the finalcopper plate directly to the pickled surface of said objects to which aquantity of pickling bath solution remains adherent by electroplatingsaid objects in an acid solution of a copper salt, said solutioncontaining a brightening agent and an inhibitor.

7. The method of producing copper deposits on surfaces of metal objects,said metal being selected from the group consisting or iron, zinc,aluminum and electrochemically active steels, which comprises picklingsaid objects in an acid pickling bath containingN,Ndiethyldithiocanbamic acid-n-propylester-w-sodium sulfonate, andthereafter applying the final copper plate directly to the pickledsurface of said objects on which a layer of inhibitor from said picklingbath solution remains adherent by electroplating said objects in an acidsolution of copper sulfate, said solution containing small amounts ofN,N-diethyl-dithiocanbamic acid-n-propylester-w-sodiurn sulfonate.

8. The method of producing copper deposits on surfaces of objects, saidmetal being selected from the group consisting of iron, zinc, aluminumand electrochemically active steels which comprises pickling saidobjects in an acid pickling bath containing a small amount of thebetaine salt of isothiourea-S-propane-w-sulfonic acid, and thereafterapplying the final copper plate directly to the pickled objects on whicha layer of inhibitor from said pickling bath solution remains adherentby contacting said objects with an acid solution of copper sulfate, saidsolution containing the betaine salt of isothiourea-S-propane-w-sulfonicacid.

9. The method of producing copper deposits on surfaces of metal objects,said metal being selected from the group consisting of iron, zinc,aluminum and electrochemically active steels, which comprises picklingsaid objects in an acid pickling bath containing bivalent tin chlorideand N,N-pentamethylene-dithiocarbamic acidn-propylester-w-sodiumsulfonate, and thereafter applying the final copper plate directly tothe pickled objects on which a layer of inhibitor from said picklingbath solution remains adherent by contacting said objects with an acidsolution of copper sulfate, said solution containingN,N-pentamethylene-dithiocarbamic acid-n-propyb ester-w-sodiumsulfonate.

References Cited in the file of this patent UNITED STATES PATENTS2,217,921 Saukaitis Oct. 15, 1940 2,363,973 Kennedy et al Nov. 28, 19442,366,737 Loder et al. Jan. 9, 1945 2,389,181 Brown Nov. 20, 19452,410,844 Signaigo et al. Nov. 12, 1946 2,424,887 Henricks July 29, 19472,511,988 Myers et al. June 20, 1950 2,560,979 Pessel July 17, 19512,563,229 Faust et al. Aug. 7, 1951 2,700,020 Pierce Jan. 18, 19552,742,412 Cransberg et al Apr. 17, 1956 FOREIGN PATENTS 602,591 GreatBritain May 31, 1948 888,493 Germany July 8, 1949 637,453 Great BritainMay 17, 1950 OTHER REFERENCES Metal Ind., Feb. 16, 1945, page 108,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,903,403 September 8, 1959 Wennemar Strauss t' error appears in the-printed specification It is herebfi certified the quiring correctionand that the said Letters of the above numbered patent re Patent shouldread as corrected below.

Column 3, line 7, for "plate" read plating line 16, for"thiobenzooxazole" read m thiobenzoxazole line 32, for "Butyl" readbutyl column 5, lines 2'7 38, and 4% for er iron", each occurrence, readof iro.

th day of March 1960.,

and column (a, line l 9 an: a

Signed and sealed this 29 Attest: KARL Ho AXLINE ROBERT C. WATSONCommissioner of Patents Attesting Oificer

3. THE METHOD OF PRODUCING COPPER DEPOSITS ON SURFAES OF METAL OBJECTS,SAID METAL BEING SELECTED FROM THE GROUP CONSISTING OF IRON, ZINC,ALUMINUM AND ELECTROCHEMICALLY ACTIVE STEELS, WHICH COMPRISES PICKLINGSAID OBJECTS IN AN ACID PICKLING BATH CONTAINING AN INHIBITOR COMPOUNDHAVING AN INHIBITING EFFECT OF AT LEAST 50% AND THEREAFTER APPLYING THEFINAL COPPER PLATE DIRECTLY TO THE PICKLED SURFACE OF SAID OBJECTS TOWHICH A QUANTITY OF PICKLING BATH SOLUTION REMAINS ADHERENT BYELECTROPLATING SAID OBJECTS IN AN ACID SOLUTION OF A COPPER SALT.